An antenna circuit of a mobile communication terminal allows an antenna to transmit or receive predetermined radio signals. In order to optimize the transmit/receive radiation performance of the antenna, impedance matching must be exactly performed. Therefore, the antenna circuit includes capacitors and inductors, and the impedance of the antenna is matched in the optimal status by adjusting values of the capacitors and the inductors.
In general, the impedance matching of the antenna is achieved in a state that the mobile communication terminal is positioned in a free space.
Meanwhile, the mobile communication terminal may be used by a user in a state that the user grips the body of the mobile communication terminal with the hand of the user and adheres a speaker to the ear of the user due to the mechanical characteristic of the mobile communication terminal, or may be used by the user through an ear-phone in a state that the body of the mobile communication terminal is put into a pocket or a bag of the user.
As the user uses the mobile communication terminal by gripping the mobile communication terminal with the hand of the user and adhering the speaker to the ear of the user, or as the user uses the mobile communication terminal put into the pocket or the bag, the conditions for the impedance matching of the antenna may vary, so that the transmit/receive radiation performance of the antenna subject to impedance matching in the free space may be degraded.
Therefore, the mobile communication terminal employs an adaptive tuning antenna circuit to automatically adjust the impedance of the antenna when the conditions for the impedance matching of the antenna vary, so that the antenna has the optimal transmit/receive radiation performance.